Chronic postoperative pain occurs in up to 50% of patients following major surgery and up to 10% of patients following less invasive minor surgery. Invasive surgeries typically produce a larger area of tissue damage accompanied by a prolonged healing time, which may in turn induce complex spinal cord changes (central plasticity) that increase the risk for development of chronic post-surgical pain. Timely and adequate local/peripheral treatment seems a logical strategy to prevent the development of persistent postoperative pain. Migrating macrophages at the site of injury orchestrate the resolution of inflammation and wound healing by acquiring a M2 phenotype (enhancement of ED2/CD163 expression and mannose receptor expression and activity). We propose to target macrophages via mannose receptors using polyethylenimine (PEI) nanoparticles grafted with a mannose ligand (Man-PEI) to induce ED2/CD163 gene expression. This state-of- the art nanotechnology approach has been used successfully to treat HIV-positive patients, supporting the translational value of this proposal. We have shown that genetic induction of ED2/CD163 using nanoparticles in murine monocytes induced an anti-inflammatory cellular phenotype characterized by a reduction of mitogen activated protein kinase (MAPK) activation, namely ERK), p38, and p- Jun-amino-terminal kinase (p-JNK), and pro-inflammatory cytokine release. In patients, the regulation of MAPKs reduces acute postoperative and chronic neuropathic pain, which adds clinical relevance to our studies. We hypothesize that the induction of ED2/CD163 gene in human macrophages using mannosylated nanoparticles will reduce the activation of ERK, p38 and JNK, and the release of pro-inflammatory effectors, which will prevent the development of persistent postsurgical pain in a rat model. We will follow these specific aims: 1) Optimization of nanotechnology-based ED2/CD163 induction in human macrophages (efficiency of transfection and gene induction); 2) Assessment of nanotechnology-based ED2/CD163 induction in macrophage response patterns following LPS or interleukin (IL)-6-stimulated inflammation (reduction of MAPK activation and re-balance of pro- and anti-inflammatory factors); 3) Determination of the behavioral and molecular effects of in vivo ED2/CD163 induction using nanoparticles in a rat model of persistent postsurgical pain (prevention of postoperative pain by inducing an anti-inflammatory phenotype in surgical macrophages). These studies will set the foundation for testing this technology in clinical trials in patients undergoing major surgeries. This is a grant composed by a team of clinical and basic researchers in nanotechnology and pain. It proposes novel, innovative and highly translational research under the direction of a productive NIH funded investigator who has relocated to an AREA eligible school to help build a culture of biomedical and health- related research. This proposal has been designed to provide undergraduate students with high quality biomedical research experiences that will prepare the students for biomedical sciences graduate programs. extracellular signal-regulated kinase (